bytes vs bitmapData

[Edward Hillenbrand]

I'm loading an image into a NSBitmapImageRep object and a NSData object,
but when I get the raw data using -bitmapData and -bytes they appear to
be different, at least when loaded as an OpenGL texture. What is the
difference between NSBitmapImageRep's -bitmapData and NSData's -bytes?
And why is there a difference?

[James Weatherley]

In article <20030827204605328-0700@news.sf.sbcglobal.net>,
[email]elihREMOVE@sbcREMOVEglobal.net[/email] says...

> I'm loading an image into a NSBitmapImageRep object and a NSData object,
> but when I get the raw data using -bitmapData and -bytes they appear to
> be different, at least when loaded as an OpenGL texture. What is the
> difference between NSBitmapImageRep's -bitmapData and NSData's -bytes?
> And why is there a difference?
>

If you load a file into NSData then 'bytes' will give you the bytes from
the file a bit like loading the image into a hex editor so you'll have
all the file headers, preview images, padding, comments, compressed
data, etc. Unless you're interested in the file rather than the image
this is probably not what you want.

When loaded into an NSBitmapImageRep you are given access to the image
data as it will be displayed on the screen. You can then use the methods
for getting information about the image to examine or alter the pixels.
'bitmapData' will give you a pointer to the start of the pixels and
using methods like 'bitsPerPixel', 'bytesPerRow' and 'samplesPerPixel'
will allow you to determine how the data is stored within the array
returned from 'bitmapData'.